Implementation of distributed high precision real-time data acquisition system

For high precision acquiring of low-frequency vibration signal in large-scale area, a data acquisition system employing serial chain structure is implemented. Four data acquisition channels which are based on 24-bit sigma-delta modulator CS5372 and digital filter CS5376A are implemented on each acquisition node. Excellent analog performance with circuit noise less than 1.6 muV and total harmonic distortion less than -106 dB is achieved and verified by careful measurement. An ARM7 processor and a free real time operating system freertos are employed for system management of acquisition node to realize real-time data acquisition. To guarantee simultaneous sampling and recording of various acquisition nodes which are apart from each other, precise synchronization signals and configuration commands for acquisition nodes are transmitted over half-duplex RS-485 bus, while FPGA on acquisition node classifies and decodes these signals. Signal and power supply share the RS-485 bus to minimize cables between acquisition nodes, thus system cost is reduced while the reliability is greatly improved.